The Yarkovsky orbital evolution effect, due to the recoil force
arising from anisotropic re-radiation of sunlight, is most effective
for bodies in the diameter range 0.1-10 m, and depends in a
complex way on the spin state and thermal properties of the affected
bodies. This mechanism can explain why meteorite CRE ages (in
particular for irons) are much longer than the dynamical lifetimes of
bodies delivered to Earth-crossing orbits through resonances. Thanks
to the Yarkovsky effect, small main-belt asteroid fragments undergo a
slow decay in semimajor axis and have enough mobility to reach the
resonances after relatively long times spent in nonresonant orbits.
Also, since metal-rich bodies have longer collisional lifetimes, they
can drift much farther and this explains why they appear to come from
a larger number of asteroid parent bodies compared to ordinary
chondrites. The figure shows the (numerically integrated) orbital
evolution of a 5-m stony object drifting into the 3:1 resonance and
having its eccentricity pumped up to Sun-grazing values after
13 Myr.